Variable-rate application of inputs makes good sense

FRIARS POINT, Miss. — For Tripp Hayes, variable-rate technology means he doesn’t have to compromise chemical rates. For John Bassie, it could mean more efficient soil sampling. For John McKee, the new technology just makes good sense.

Cotton producers Hayes, Clarksdale, Miss., and McKee, Friars Point, Miss., and Bassie, a Cleveland, Miss., consultant, spoke of their experiences with variable-rate technology during a precision ag field tour on McKee’s Westside Farms in November. The event was held in conjunction with Cotton Incorporated’s Crop Management Seminar in Tunica.

The producers’ and consultant’s variable-rate production programs begin with high resolution aerial photographs that measure the variability of crop health within their fields. The digital infrared images are converted into scout maps that correlate to different levels of plant biomass in the fields. The images are available through In-Time, Inc., a Web-based, variable-rate service based in Cleveland, Miss.

The scout map can be transferred to a handheld computer equipped with a GPS receiver, which allows the user to walk a field and visually document plant health in specific areas, also called zones.

Once a field is scouted, rate recommendations are made for each individual class of plant vigor as indicated by the map. In-Time can convert the map image to a variable-rate prescription that can be accessed via the Internet. That information is transferred to the farmer’s or aerial applicator’s variable-rate equipment.

The maps can show differences in plant vigor not visible to the naked eye, according to Hayes. “When we began using the service three years ago, (consultant) Joe Townsend and I walked into a field to write our first prescription for variable-rate application.

“We couldn’t see any difference whatsoever between Zones 7 and 6. Finally, we pulled up a plant and counted the nodes. There was one node difference between the two zones. Infrared photography picked that up.”

Bassie said the scout maps are reliable indicators of plant health. “A Zone 7 in field 16 is going to be the same as Zone 7 in fields 5, 8 and 12. I also think that if you took soil samples from each Zone 7, the samples would be similar.”

This implies that the farmer or consultant armed with scout maps could reduce the number of soil samples significantly, perhaps to several samples for each of seven zones represented.

Hayes, who farms about 3,200 acres of cotton with his father, Stan, has learned three things from his variable-rate experience.

“The technology definitely works. The only problem you might have is when there is cloud cover, you can’t get a picture. Soil variability is going to determine how useful it’s going to be for you. The key is the person writing the prescription, who in my case is my consultant.”

McKee added, “If I don’t have a consultant who is on-board with it, I can’t use it. I don’t have time to be out in the field writing prescriptions.”

A variable-rate applicator equipped with GPS can also create an as-applied map, which shows how inputs were applied on the field. “I have never seen an as-applied map that didn’t agree with the prescription,” Hayes said.

This year, Hayes made variable-rate applications for insecticides (plant bugs), plant growth regulators and defoliants. “We’ve also made some variable-rate applications on tobacco budworm. This has a lot of potential. We have been growing 20 percent non-Bt cotton. If we can cut our budworm expense by 40 to 50 percent in those areas, that makes it much more viable for alternatives to Bt cotton.

“Defoliation is where we get the biggest bang for our buck,” Hayes said. “For the last two years, we’ve picked 10 to 11 days after variable-rate defoliation. “Our practice in the past has been two (blanket) applications, and it would normally be 14 days before the crop was ready from one end of the field to the other.”

Infrared imagery has isolated pockets of nematode infestations in fields, according to Hayes. “We plan to use an applicator (applying Temik) with a scout map and drop in the nematode spots. I’m convinced we can make that work.”

Hayes said he’s managing inputs more efficiently with variable-rate technology. “We’ve been managing the whole farm for the middle 40 percent of the field rather than for the good land. This technology helps minimize that compromise. In a conventional situation, you would have compromised. You would have come up with an average rate.”

“We found that what we thought was our best soil has not been producing our best cotton,” Bassie added. “Our middle class soil has been producing our best cotton. We have to do more work in our top soils to get yield up.”

McKee said it’s difficult to quantify the benefits of variable-rate technology, but that “it makes good sense. My intuition tells me that I’m going to do it again next year. I see it every day from the turnrow, and I just think it’s paying me.”

Variable-rate technology “is part of what we do now,” McKee said. “It’s not difficult. I won’t go back. The learning curve wasn’t that hard to get over, and I think we’re there now.”

Bassie said the program can give growers a head start on controlling insects. “We know that insects have certain habits. Aphids and beet armyworms love drought-stressed cotton. The image can show you where the thin cotton is. Budworms and bollworms like the healthy cotton.”

Likewise, “when plant bugs enter the field, they go to the best cotton. We can kill them there and spray on time. Don’t give them a chance because they’re not going to give you one.”

Bassie said that timing of applications and interpreting imagery are the most important parts of a variable-rate program. The only way to do the latter is to “get out in the field, whether it’s muddy or dry,” Bassie said.

Bassie is convinced the technology can give him and his growers a new tool for generating profit. “I don’t want to go to the field without that scout map.”